1. Field of the Invention
The present invention relates to a device for determining the centering data for eyeglass lenses, i.e., to adjust optical lenses to the parameters of a specific eyeglass frame.
2. Description of the Prior Art
Among the various parameters which must be adjusted to fit the eyeglass lenses correctly in the eyeglass frame and to make the optical centers of the lenses coincide with the visual axes of the eyes, it is usual to know the pupillary distance and the level of the pupils with respect to the eyeglass frame.
It is also important to measure the level of the optical centers of the lenses with respect to the lower and upper edges of the eyeglass frame into which they are to be fitted.
The usual routine procedure employed by the opticianxe2x80x94and thus the currently accepted prior artxe2x80x94is one in which the optician and client sit opposite one another and the client puts on a frame of his choice containing a glass disk. The client is then requested to xe2x80x9clook at a distant point,xe2x80x9d after which the optician draws a hatch mark, based on visual judgment, on the disk or a ruled contrast film at the viewing reference point which has been sighted from the visual reference opposite the client. The centering hatch mark determines the position of the optical center of the eyeglass lens to be set in the frame.
This procedure is followed individually for each eye (monocular approach)xe2x80x94with the result that one obtains, essentially empirically, the pupillary distance PDxe2x80x94including, however, all possible attendant imprecision from parallax, marking errors, etc.
The present invention is a device which allows for a rapid and practicably precise determination of the necessary eyeglass lens centering data.
According to the invention, this goal is achieved by a device for determining the eyeglass lens centering data, the device including a housing which is height-adjustable by means of a lift column, the housing supporting a digital video camera in which the objective lens together with a mirror and a light source is located in the region of the front panel of the housing; and including a digital computer connected to the digital video camera, wherein the client may take up a marked position, preferably one approximately 3 m distant, with the already-selected eyeglass frame in front of the mirror, and wherein a superposable frame is mountable on the eyeglass frame, the superposable frame being equipped with a sighting device with a scale from which the tilt of the eyeglasses is readable, the head position of the client and tilt of the eyeglasses being monitorable at the computer on the monitor screen, and wherein the superposable frame has two calibration points at a predetermined spacing which matches the average distance between the eyes, the exact position of the calibration points being quickly and precisely determinable by an essentially automated computer program on the monitor screen after freezing the client image by controlling the individual calibration points by a square box appearing automatically on the screen and subsequently automatically determining the brightness center point of the calibration points, the exact position of the two reflection points of the light source on the cornea imaged on the screen also being quickly and precisely determinable analogously in a subsequent program step by controlling the square box.
The device according to the invention is distinguished specifically by the fact that the determination of data by using the reflection points of the light source at the apex of the cornea of the right and left eye is effected very precisely. These reflection points are obtained as an essentially point-type reflected image of the light source at the apex of the cornea. The light source of the device according to the invention consists preferably of a ring illuminator which surrounds the edge of the mirror which is designed as a circular mirror. The above light source may also consist of two Illuminators which are located on each side of the mirror edge, approximately at the level of the objective lens of the video camera, or preferably approximately at a level immediately above the upper edge of this objective lens.
The sighting device of the superposable frame advantageously has an on-off-switchable locating illuminator, specifically in the form of a light-emitting diode, as well as a diffusing screen with a scale in front of which a preferably spherical bead of the sighting device is located at a predetermined distance of approximately 20 mm, wherein an essentially point-type shadow on the scale of the sighting device is created when the spherical bead is illuminated, the shadow being employed to read the tilt angle of the eyeglasses, and wherein a horizontal line of the scale, which line preferably matches the approximately 11xc2x0 tilt angle of the eyeglasses and is emphasized in thickness as the reference line, and wherein the additional horizontal scale lines above and below this reference line each represent a change in the eyeglass tilt angle of approximately 5xc2x0. The locating illuminator on the superposable frame ensures that the client gazes at the reflected image of the illuminating locating illuminator in the mirror at a preferred measurement distance of 3 m between the client and mirror, and thus at a real distance of 6 m, thereby meeting the requirement of viewing with a relaxed focus; in addition, this measurement may be performed in the examination room or in ancillary rooms without interfering with general client traffic.
The rapidity of the measurement procedure is achieved by the fact that the computer is programmed so that the individual measurement steps proceed essentially automatically and upon completion of a given step the tools and aids required for the next step automatically appear on the monitor screen. The operator is thus guided through the measurement program, thereby accelerating the measurement procedure.
The main emphasis has been laid specifically upon the fast and practicably precise determination of the required centering data. An extremely important factor is the fact that operation is simple and may be performed by any employee after a brief training period. These requirements were able to be met by the device according to the invention which is not based on the previous method of measurement. The invention is based on utilizing the cornea reflection of a light source located at a distance of 3 meters. This reflection provides a precise reference point for determining the centering data, whereas the determination of the measurement data based on the edge of the iris provides only estimated values. In the device according to the invention, preferably a plurality of preferably approximately 10xc3x9710 to 20xc3x9720 pixels on the computer screen are selected when determining the brightness center point of the calibration points for the superposable frame and/or of the reflection points of the light source on the cornea of the eye using the square box, only those pixels of the square box being selected to determine the brightness center point for which the brightness lies above an externally selectable threshold, and the evaluation proceeding by way of a weighted averaging in which a first sum is obtained from the brightness of the selected pixels multiplied by the X-coordinate, a second sum from the brightness of the selected pixels multiplied by the Y-coordinate, and a third sum from the brightness of selected pixels, the X-coordinate of the brightness center point resulting from division of the first sum by the third sum, and the Y-coordinate of the brightness center point resulting from division of the second sum by the third sum.